This invention relates to a vacuum insulating glass (IG) unit, and a method of making the same.
Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
Prior art FIGS. 1-2 illustrate a conventional vacuum IG unit. IG unit 1 includes two spaced apart glass substrates 2 and 3 which enclose an evacuated or low pressure space 6 therebetween. Glass sheets/substrates 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and an array of support pillars or spacers 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between substrates 2 and 3 can be evacuated to create a low pressure area or space 6. After evacuation, tube 8 is melted to seal the vacuum. Recess 11 retains sealed tube 8. Optionally, a chemical getter 12 may be included within recess 13.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal 4) is initially deposited around the periphery of substrate 2. The other substrate 3 is brought down over top of substrate 2 so as to sandwich spacers 5 and the glass frit/solution therebetween. The entire assembly including sheets 2, 3, the spacers, and the seal material is then heated to a temperature of approximately 500xc2x0 C. at which point the glass frit melts, wets the surfaces of the glass sheets 2, 3, and ultimately forms hermetic peripheral or edge seal 4. This approximately 500xc2x0 C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal 4 and the seal around tube 8, the assembly is cooled to room temperature. It is noted that column 2 of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500xc2x0 C. for one hour. Inventor Collins of the ""395 patent states in xe2x80x9cThermal Outgassing of Vacuum Glazingxe2x80x9d, by Lenzen, Turner and Collins, that xe2x80x9cthe edge seal process is currently quite slow: typically the temperature of the sample is increased at 200xc2x0 C. per hour, and held for one hour at a constant value ranging from 430xc2x0 C. and 530xc2x0 C. depending on the solder glass composition.xe2x80x9d After formation of edge seal 4, a vacuum is drawn via the tube to form low pressure space 6.
Unfortunately, the aforesaid high temperatures and long heating times utilized in the formulation of edge seal 4 are undesirable, especially when it is desired to use a tempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown in FIGS. 3-4, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis in FIG. 4 extends from zero to one hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (F.). The different curves/lines are 400xc2x0 F. (across the top of the FIG. 3 graph), 500xc2x0 F., 600xc2x0 F., 700xc2x0 F., 800xc2x0 F., 900xc2x0 F., and 950xc2x0 F. (the bottom curve of the FIG. 3 graph). A temperature of 900xc2x0 F. is equivalent to approximately 482xc2x0 C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2. Thus, attention is drawn to the 900xc2x0 F. curve in FIG. 3, labeled by reference number 18. As shown, only 20% of the original temper strength remains after one hour at this temperature (900xc2x0 F. or 482xc2x0 C.). Such a significant loss (i.e., 80% loss) of temper strength is of course undesirable.
In FIGS. 3-4, it is noted that much better temper strength remains in a thermally tempered sheet when it is heated to a temperature of 800xc2x0 F. (i.e., about 428xc2x0 C.) for one hour as opposed to 900xc2x0 F. for one hour. Such a glass sheet retains about 70% of its original temper strength after one hour at 800xc2x0 F., which is significantly better than the less than 20% when at 900xc2x0 F. for the same period of time.
Another advantage associated with not heating up the entire unit for too long is that lower temperature pillar materials may then be used. This may or may not be desirable in some instances.
It will be apparent of those of skill in the art that there exists a need for a vacuum IG unit, and corresponding method of making the same, where a structurally sound hermetic edge seal may be provided between opposing glass sheets without at least certain portions of thermally tempered glass sheet(s)/substrate(s) of the IG unit losing more than about 50% of original temper strength. There also exists a need in the art for a vacuum IG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with a conventional vacuum IG manufacturing technique where the entire unit is heated in order to form a solder glass edge seal. It is a purpose of this invention to fulfill one or more of the above listed needs in the art.
An object of this invention is to provide a vacuum IG unit having a peripheral or edge seal formed so that at least certain portion(s) of thermally tempered glass substrates/sheets of the IG unit retain more of their original temper strength than if conventional edge seal forming techniques were used with the solder glass edge seal material.
Another object of this invention is to provide a vacuum IG unit, and method of making the same, wherein at least a portion of the resulting thermally tempered glass substrate(s) retain(s) at least about 50% of original temper strength after formation of the edge seal (e.g., solder glass edge seal).
Another object of this invention is to reduce the amount of post-tempering heating time necessary to form a peripheral/edge seal in a vacuum IG unit.
Yet another object of this invention is to form a hermetic edge seal in a vacuum IG unit by utilizing microwave energy to cure edge seal material. In an exemplary embodiment, glass frit suspended in liquid or solution may be deposited as an edge seal base material on each of first and second annealed glass substrates (e.g., soda-lime-silica float glass substrates). This may be referred to as an initial or first glass frit application. Each of the glass substrates may then be thermally tempered with the edge seal material thereon so that during the thermal tempering process, the edge seal material at least partially diffuses into and/or bonds to the respective glass substrates. This fuses the glass frit edge seal material to the glass substrates (i.e., pre-firing the first glass frit application) while at the same time tempering the substrates. Thereafter, a second application of glass frit may be applied to one or both of the substrates over the pre-fired first glass frit application. Spacers and/or pillars may be sandwiched between the substrates as the substrates are brought together. Then, microwave energy is directed toward the edge seal material in order to heat the same (i.e., heating at least the second glass frit application, and preferably both the first and second glass frit applications) thereby causing the second glass frit edge seal material to fuse to, or bond with, the first or pre-fired glass frit base material on both substrates thereby creating a hermetic edge seal.
In certain embodiments, the first application of glass frit edge seal material is deposited on the respective substrates prior to thermal tempering, because diffusion of solder glass or glass frit into an annealed non-tempered glass substrate may be easier than diffusion of solder glass or glass frit into a tempered glass substrate. Thus, by causing the edge seal material to fuse into the glass substrate(s) during the tempering process yet prior to full tempering of the substrate(s), a better bond of the edge seal to the substrate(s) may be achieved.
Moreover, the use of microwave energy (localized or otherwise) in order to form an edge seal (e.g., using the second glass frit application) enables one or both of the thermally tempered glass sheets/substrates to retain much temper strength because at least certain portions (e.g., central portions) of the glass substrate(s) need not be heated along with the solder glass edge seal material during formation of the edge seal. Moreover, the use of microwave energy in forming the edge seal of a vacuum IG unit can result in reduced processing time as well as a reduced need for capital intensive manufacturing equipment such as ovens, furnaces, or the like.
Another object of this invention is to fulfill one or more of the above listed objects and/or needs.
Generally speaking, certain embodiments of this invention fulfill one or more of the above-listed needs and/or objects by providing a method of making a thermally insulating unit, the method comprising:
providing first and second substrates with a plurality of spacers therebetween; and
forming a hermetic peripheral or edge seal at least partially between the first and second substrates using at least microwave energy.
Certain embodiments of this invention further fulfill one or more of the above-listed needs by providing a method of making a thermally insulating glass panel, the method comprising:
depositing a first portion of edge seal material on first and second glass substrates;
thermally tempering the first and second glass substrates with the first portion of edge seal material thereon;
following said tempering, depositing a second portion of edge seal material on at least the first substrate over at least part of the first portion of edge seal material already on the first substrate;
forming a hermetic peripheral or edge seal at least partially between the first and second substrates by at least using microwave energy directed toward at least the second portion of edge seal material so that the second portion of edge seal material bonds to both: a) the first portion of edge seal material on the first substrate, and b) the first portion of edge seal material on the second substrate; and
evacuating a space between the first and second substrates so as to form a low pressure area having a pressure less than atmospheric pressure between the first and second substrates.
Certain other embodiments of this invention fulfill one or more of the above-listed needs by providing a thermally insulating panel comprising:
first and second spaced apart substrates having a low pressure space therebetween having a pressure less than atmospheric pressure;
a hermetic seal provided between said first and second substrates; and
wherein said seal includes first and second solder glass or glass frit seal portions, at least a portion of said first seal portion having been deposited on said first substrate prior to tempering thereof and said second seal portion having been deposited on one of said substrates following tempering thereof.